Osteosynthetic bone plate

ABSTRACT

The invention relates to an osteosynthetic bone plate which has elongated compression cavities containing eccentric countersinkings. The plate comprises a longitudinal axis (X), a transverse axis (Y), a plate upper side and a plate lower side, whereby the latter is placed facing the bone fragments. The bone plate also comprises a compression element consisting of two plate braces which run substantially parallel to the longitudinal axis. Both plate braces are linked together by bridging struts which intersect the longitudinal axis. A plate brace has an eyelet on at least one of the outer sides of the compression element. Additional eyelets can be positioned in front of this eyelet. A compression cavity is situated in each of said eyelets and a connecting strut which intersects the transverse axis, extends between the eyelets which are located on each plate brace.

FIELD OF APPLICATION OF THE INVENTION

The present invention relates to an osteosynthetic bone plate for thetreatment of fractures, in particular for the reconstruction ofmandibular fractures. Such bone plates are fitted intraoperatively inorder to fix bone fragments joined together. This may be necessary inosteosynthesis, following accidents in which a bone has shattered intobone fragments, or in orthognathic, maxillofacial treatment for surgicalcontrol of abnormal positioning after an osteotomy and subsequentpositional correction of the bone fragments.

Such a bone plate is used principally to span and fix two bone fragmentstogether, one part of the bone plate in each case being connectedreleasably to a bone fragment. In order to establish the connectionbetween the temporarily fitted bone plate and the bone fragments, thebone plate has through-holes for the insertion of bone screws whichengage in the bone fragments. The bone plates should be able to bend inorder to correctly match the bone geometry, but at the same time theymust guaranatee sufficient stability. These two requirements are inprinciple mutually contradictory. Moreover, the bone plates shouldpermit the buildup of a pressure between the fragments, which isachieved by the opposite arrangement of what are referred to ascompression holes.

PRIOR ART

DE 23 40 880 A1 discloses a solid linear bone plate which is used fortreating jaw fractures and which, spanning the fracture site on the jawbone, is screwed onto both of the bone fragments that are to be joinedtogether. In each half of the bone plate there are two oblong holesoriented toward the plate center and toward the fracture site. On theside directed away from the jaw bone, the oblong holes have acountersink with a screw seat configured as a beveled plane surface. Atleast one oblong hole per half is inclined relative to the plate center.On the side directed toward the jaw bone, the bone plate has aprojecting notched strut at the center. As a result of the arrangementof the oblong holes and the beveled screw seats, the bone fragments arecompressed toward the fracture site when the inserted bone screws aretightened; the pressure thus built up between the fragments results inimproved healing of the bone fracture.

However, because of its rigidity, this plate cannot readily be adaptedto the existing bone geometry. A rigid plate which cannot besufficiently bent to fit the jaw bone has the effect that the bonefragment less anchored in the jaw is moved toward the plate, anddislocations therefore occur. Even slight shifts in the fracture arealead to the loss of the interfragment support, which results in greatermobility within the fracture area. The simple hole pattern on the plateadditionally permits little variability in terms of attachment to thebone fragments. For example, in Prein, J. (editor): Manual of InternalFixation in the Cranio-Facial Skeleton, Springer-Verlag Berlin 1998,page 30, straight or arcuate bone plates with compression holes fortreating fractured mandibles are shown which have a thickness of 1.65 mmor 2.0 mm, respectively, and are designed for bone screws with anexternal thread diameter of 2.4 mm.

Thinner bone plates, for example with a thickness of between 0.5 mm and0.9 mm, which can be bent more readily, are known in craniofacialapplications (cf. Prein, loc. cit., page 28). Different configurationshave been developed for this purpose, for example the L-plate, Y-plate,T-plate, H-plate, X-plate, double Y-plate or frame plate. Bone screwswith an external thread diameter of 1.0 mm to 2.0 mm are used for these.However, these bone plates have no compression holes, but only simplecylindrical screw holes with countersinks for partially receiving thescrew head. The provision of compression holes in these thinner plateshas been avoided because opinion hitherto held that a greater platethickness, for example 1.65 mm or 2.0 mm, was necessary for building upa pressure between the fragments. In addition, with the previouslyavailable production technology, it would have been extremelycomplicated to work compression holes into thinner bone plates, forexample with the thickness of 1.0 mm.

OBJECT OF THE INVENTION

According to the prior art hitherto disclosed, no bone plate has as yetbeen made available in which, even when absolutely correctly applied,sufficient stability for unimpeded bone healing is guaranteed and apressure can be built up between the fragments for the dynamiccompression for improved bone fracture healing. Particular requirementsexist for example in respect of:

-   -   fractures of atrophic jaws;    -   unstable oblique fractures;    -   infected mandibular fractures;    -   unstable jaw angle fractures; and    -   mandibular fractures in noncooperative patients.

In view of the cited shortcomings of the bone plates known to date, theobject of the invention is to make available a bone plate particularlyfor the treatment of mandibular fractures, which, as a result of greaterdeformability, can be readily bent to the respective contour of the bonefragments, but which nevertheless guarantees a secure and positionallystable fixation of the bone fragments. That is to say, the bone platemust be easily deformable on the one hand and yet must have adequaterigidity on the other. Moreover, the bone plate is to have compressionholes in order to be able to generate a pressure between thefragments—in the sense of compression osteosynthesis—for promoting thebone healing. Furthermore, the bone plate to be produced must not pinchthe nerve issuing at the mandible and, in the event of comminutedfractures, small bone fragments must also be able to be fixedindividually on the bone plate. Finally, the bone plate must be able tobe applied using conventional bone screws and must be able to beproduced economically in series.

OVERVIEW OF THE INVENTION

The osteosynthetic bone plate is used for the treatment of fractures, inparticular for the reconstruction of mandibular fractures. The plate isintended to be screwed by means of conventional bone screws, which havescrew heads, onto the bone fragments which are to be joined together inaccordance with the principle of compression osteosynthesis at afracture line. The plate has oblong compression holes with eccentriccountersinks. A longitudinal axis and a transverse axis, and also aplate upper side and a plate lower side, the latter facing toward thebone fragments, can be defined on the plate. The bone plate comprises acompression part which has two plate braces extending at leastsubstantially parallel to the longitudinal axis. The two plate bracesare connected to one another by bridging struts which intersect thelongitudinal axis. A plate brace has an eyelet at least on one of theouter flanks of the compression part, and additional eyelets can bepositioned in front of this eyelet. An eyelet is preferably arranged onboth outer flanks. A compression hole is preferably situated in each ofthe eyelets, and a connecting strut which intersects the transverse axisextends between the eyelets located on each plate brace.

The following description refers to preferred illustrative embodimentsof the bone plate according to the invention: The compression holeshave, with their longitudinal extent, an orientation in the direction ofthe brace axis or assume an angle ≠ 0° in relation to the brace axis andhave eccentric countersinks on the plate upper side. In a continuationof the compression part, attachment struts adjoin the eyelets and extendon the brace axes. A disk-shaped plate member is situated at the end ofeach of the attachment struts, and further plate members connected byattachment struts can be positioned in front of said plate member. Afixation hole for receiving a bone screw is in each case provided in theplate members.

The connecting struts between the eyelets have a greater width than theattachment struts leading to the plate members. The fixation holes onthe plate upper side have a countersink for receiving the heads of thebone screws in a partially recessed manner. Two bridging struts arepreferably provided on the bone plate and extend symmetrically orasymmetrically with respect to the transverse axis. In the case of asymmetrical arrangement of the bridging struts, both bridging strutsextend laterally from the outer flank of one eyelet on one brace axis tothe outer flank of the opposite eyelet on the other brace axis. In thecase of an asymmetric arrangement of the bridging struts, by contrast,one bridging strut is offset toward the transverse axis and, as seenfrom the latter, extends in front of the pair of eyelets which lieopposite each other on the two brace axes.

The bone plate has a material thickness in the range from 0.5 mm to 1.5mm and is preferably made of titanium of quality grade 1 or grade 2. Thebone screws inserted in the compression holes and in the fixation holesare provided for monocortical screwing to the bone fragments.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

FIG. 1A shows a plan view of a symmetrical bone plate with 4 compressionholes and 4 cylindrical fixation holes;

FIG. 1B shows the view according to FIG. 1A, in a cross section alongthe line A-A;

FIG. 2 shows a plan view of an asymmetrical bone plate with 4compression holes and 4 cylindrical fixation holes;

FIG. 3 shows a plan view of a symmetrical bone plate with 4 compressionholes;

FIG. 4 shows a plan view of a symmetrical bone plate according to FIG.1A with 2 compression holes oriented at an angle to the longitudinalaxis;

FIG. 5A shows the symmetrical bone plate according to FIG. 3 at thestart of compression osteosynthesis with an open bone fracture;

FIG. 5B shows the view according to FIG. 5A during compressionosteosynthesis with a closed bone fracture;

FIG. 6A shows the symmetrical bone plate according to FIG. 3 fittedlaterally on the mandible with a jaw angle fracture;

FIG. 6B shows the symmetrical bone plate according to FIG. 1A fittedlaterally on the mandible with a jaw angle fracture;

FIG. 7A shows the symmetrical bone plate according to FIG. 1A fittedfrontally on the mandible with a median fracture; and

FIG. 7B shows the asymmetrical bone plate according to FIG. 2 fittedlaterally on the mandible with a paramedian fracture.

ILLUSTRATIVE EMBODIMENTS

In the following detailed description of illustrative embodiments of theosteosynthetic bone plate according to the invention, reference is madeto the attached drawings.

FIGS. 1A and 1B

The bone plate 1 constructed symmetrically in relation to thelongitudinal axis X and the transverse axis Y has two plate braces 2running parallel to the longitudinal axis X and spaced apart from oneanother. The plate braces 2 extend along the brace axes Z. Each platebrace 2 ends at the outside with a disk-shaped plate member 3, at thecenter of which a cylindrical fixation hole 4 is provided which, on theplate upper side 5, has a countersink 7 for receiving a screw head in apartially recessed manner. The fixation hole 4 opens out cylindricallyon the plate lower side 6, which faces toward the bone fragments thatare to be joined. From the plate members 3, an attachment strut 8extends along each of the brace axes Z toward the transverse axis Y.

The four attachment struts 8 each adjoin an eyelet 9 of the compressionpart 10 of the bone plate 1. Provided in each eyelet 9 there is anoblong compression hole 11 of conventional contour whose longitudinalextent lies on the brace axis Z. Toward the transverse axis Y, theindividual compression hole 11 has, on the plate upper side 5, acountersink 12 which runs out harmonically in the compression hole 11increasingly away from the transverse axis Y. Thus, a bone screw fittedas it were eccentrically in the compression hole 11 is pressed in aknown manner toward the transverse axis Y with its head penetrating intothe compression hole 11 and in so doing entrains the screwed-on bonefragment with it. If the bone screws are positioned symmetrically to thetransverse axis Y, the bone fragments which are to be joined togetherare pressed on each other in the sense of compression osteosynthesis.

Extending between the eyelets 9 on both sides of the transverse axis Yon a plate brace 2 there is a connecting strut 13 which runs on thebrace axis Z and connects the two eyelets 9 to each other. Compared tothe attachment struts 8, the connecting struts 13 have a greater widthand for this reason they also have a higher degree of rigidity. The twoplate braces 2 are connected to one another by two bridging struts 14symmetrical to the transverse axis Y. The bridging struts 14 each extendlaterally from the junction of the attachment strut 8 with one eyelet 9on one brace axis Z to the junction of the attachment strut 8 with theopposite eyelet 9 on the other brace axis Z. As the bone plate 1, with athickness of for example 1.0 mm, is made of titanium of quality grade 1or grade 2 with two plate braces 2 and the bridging struts 14, the boneplate 1 can be bent to correctly match the respective geometry of thebone fragments and it also has sufficient rigidity for positionallystable fixation of the bone fragments.

FIG. 2

The difference from bone plate 1 in FIG. 1 is that in the bone plate 1shown here the bridging struts 14 connecting the two plate braces 2 arearranged asymmetrically with respect to the transverse axis Y. The rightbridging strut 14 again extends laterally from the junction of theattachment strut 8 with an eyelet 9 on one brace axis Z to the junctionof the attachment strut 8 with the opposite eyelet 9 on the other braceaxis Z. By contrast, the left bridging strut 14 is offset toward the Yaxis; this bridging strut 14 extends laterally from in front of thejunction of the connecting strut 13 with one eyelet 9 on one brace axisZ to a position in front of the junction of the connecting strut 13 withthe opposite eyelet 9 on the other brace axis Z. A bone plate 1configured in this way is primarily of use for application to aparamedian fracture of the mandible, where the issuing nerve must not bepressed by a plate part (see description of FIG. 7B).

FIG. 3

In this simplified bone plate 1, only the compression part 10 isprovided. The outwardly directed attachment struts 8 and the platemembers 3 at the very outer ends with the fixation holes 4 are notpresent here. As in the embodiment according to FIG. 1, the bridgingstruts 14 in principle extend from the outer flank of one eyelet 9 onone brace axis Z to the outer flank of the opposite eyelet 9 on theother brace axis Z. An illustrative application of this bone plate 1 isdescribed with reference to FIG. 6A.

FIG. 4

The particular feature of this symmetrical embodiment compared to thebasic embodiment according to FIG. 1 is that the two oblong compressionholes 11 with the eyelets 9 on the lower plate brace 2 do not extendlongitudinally on the brace axis Z or parallel to the longitudinal axisX, but assume the angle α . This is useful in cases where, in a specialfracture pattern, a pressure between the fragments is to be built upextending obliquely from the lower plate brace 2 to the longitudinalaxis X.

FIGS. 5A and 5B

The two figures illustrate the principle of compression osteosynthesisusing a bone plate 1 according to FIG. 3 by way of example.

In the starting situation (see FIG. 5A), the fracture line 22 to beclosed is present between the two bone fragments 20, 21 to be joined,and the bone plate 1 is to be placed with its compression part 10 acrossthis line. The bone plate 1 is of the type referred to as mini plates.The bone screws 30 are introduced into the oblong compression holes 11,directed away from the countersinks 12, i.e. at the greatest possibledistance from one another as viewed on the respective plate brace 2 andthe associated brace axis Z. As can be seen, the screw heads 31 of thebone screws 30 are screwed preferably monocortically into the bonefragments, i.e. farther away from the fracture line 22 and thetransverse axis Y.

FIG. 5B shows that, as the bone screws 30 are screwed farther into thebone fragments 20, 21, the screw heads 31 come to lie in thecountersinks 12—as a result of the specially contoured countersinks 12in the compression holes 11. The bone fragments 20, 21 hanging on thebone screws 30 are entrained in the direction of the transverse axis Yand the fracture line 22 until finally the fracture line 22 is closedand the bone fragments 20, 21 are joined together with compression.

FIGS. 6A to 7B

This sequence of figures illustrates examples of some applications ofdifferent embodiments of the bone plate 1 according to the invention inmandibular fractures.

FIG. 6A: A jaw angle fracture is treated with a bone plate 1 in theconfiguration according to FIG. 3, which only has the compression part10. The bone plate 1 fixed with four bone screws 30 spans the fractureline 22 and connects as bone fragments 20, 21 the body of the mandibleand the ramus of the mandible.

FIG. 6B: A jaw angle fracture is likewise treated with a symmetricalbone plate 1 in the configuration according to FIG. 1 which comprisesthe compression part 10 and the attachment struts 8 extending beyondthis and the outer plate members 3. The body of the mandible and theramus of the mandible are once again connected as bone fragments 20, 21across the fracture line 22. In addition to the four bone screws 30 inthe compression part 10, the bone fragments 20, 21 are secured with ineach case two bone screws 30 inserted in the outer plate members 3.

FIG. 7A: A median fracture of the mandible is treated likewise with asymmetrical bone plate 1 in the configuration according to FIG. 1, whichcomprises the compression part 10 and the attachment struts 8 extendingbeyond this and the outer plate members 3. Two parts of the broken bodyof the mandible as bone fragments 20, 21 are connected to one anotheracross the median fracture line 22. Here once again, in addition to thefour bone screws 30 in the compression part 10, the bone fragments 20,21 are fixed in a positionally stable manner with the two bone screws 30inserted in the outer plate members 3.

FIG. 7B: An asymmetrical bone plate 1 in the configuration according toFIG. 2 is used for the illustrated treatment of a paramedian fracture ofthe mandible. This bone plate 1 consists of the compression part 10, theattachment struts 8 extending beyond the latter, the outer plate members3, and the asymmetrically arranged bridging struts 14 between the twoplate braces 2. The bone plate 1 is used to connect, as bone fragments20, 21, two parts of the eccentrically broken body of the mandibleacross the paramedian fracture line 22. The emergent nerve 40 (mentalforamen) lies free and is not pinched by any of the plate parts. Thebone fragments 20, 21 are secured in each case by four bone screws 30 intotal.

1-8. (canceled)
 9. An osteosynthetic bone plate for osteosyntheticcompression of bone fragments for the reconstruction of mandibularfractures, the bone plate having a longitudinal axis and a transverseaxis and comprising: a plate upper side and a plate lower side forfacing toward the bone fragments; a compression part which has two platebraces extending at least substantially parallel to the longitudinalaxis; bridging struts, which intersect the longitudinal axis, connectingthe two plate braces to one another, each plate brace extending along abrace axis and having an eyelet on at least one outer flank of thecompression part; connecting struts, which intersect the transverseaxis, and extend between the eyelets located on each plate brace; andoblong compression holes having a longitudinal axis extendinglongitudinally along the brace axis, and eccentric countersinks on theplate upper side for the compression of the bone fragments, one of thecompression holes being situated in each of the eyelets, wherein thebone plate has a thickness in the range from 0.5 mm to 1.5 mm.
 10. Theosteosynthetic bone plate as claimed in claim 9, wherein two bridgingstruts extend symmetrically or asymmetrically with respect to thetransverse axis.
 11. The osteosynthetic bone plate as claimed in claim10, wherein in a symmetrical arrangement of the bridging struts, the twobridging struts extend laterally from an outer flank of one eyelet onone plate brace to an outer flank of an opposite eyelet on the otherplate brace, or in an asymmetric arrangement of the bridging struts, onebridging strut is offset toward the transverse axis and extends from infront of one eyelet on one plate brace to in front of the oppositeeyelet on the other plate brace.
 12. The osteosynthetic bone plate asclaimed in claim 9, wherein the bone plate is made of titanium.
 13. Theosteosynthetic bone plate as claimed in claim 9 wherein bone screwsinserted in the compression holes and in the fixation holes providemonocortical engagement of the bone fragments.